Bacterial contamination of blood products and transfusion-transmitted sepsis are two of the most important and critical untoward events in the collection, processing, storage, and infusion of blood. Great care must therefore be taken when collecting and processing blood donations in order to ensure that transfusable products are safe, and strict screening practices are employed.
Despite these preventative measures, however, bacterial contamination continues to pose a problem in transfusion medicine. For instance, the coagulase negative species Staphylococcus epidermidis is frequently implicated in severe transfusion reactions. This bacterium is known to be an important opportunistic pathogen in clinical settings due to its propensity to bind to biomedical devices, forming surface-attached communities of microorganisms known as biofilms.
Biofilm formation is a known concern in the field of medical devices, and may also contribute to undetected bacterial contamination of stored blood products. As the bacterial contaminants in the biofilm are adherent rather than planktonic, they will be difficult to detect by commonly employed methods. This is a particularly important consideration for stored blood components such as platelets.
Platelets must be stored at or above room temperature to preserve viability, conditions which allow for bacterial growth. For this reason, bacterial contamination of platelets is the most prevalent infectious risk in transfusion medicine.
Despite implementation of leukoreduction (removal of white blood cells), improved skin disinfection methods, a diversion pouch, and bacterial screening, contaminated platelet units still continue to be transfused.
Certain pathogen inactivation technologies have been developed which aim to replace the need for pre-transfusion bacterial screening. Among these, the INTERCEPT Blood System (Cerus Corp.) has completed Phase III clinical trials. This system uses amotosalen HCl, which binds to nucleic acids upon ultraviolet light (UVA) irradiation, inhibiting bacterial growth in platelets. Although this system is active against a broad variety of bacteria, it has been unsuccessful at disruption of Bacillus cereus spores and complete elimination of high loads of Pseudomonas aeruginosa and Enterobacter cloacae. Perhaps more importantly, the INTERCEPT Blood System has not been tested for the prevention and/or elimination of bacterial biofilms, which are known to be resistant to the action of antimicrobials and disinfectants.
Despite the best practices employed within the blood system and the antibacterial technologies available to prevent contamination, bacterially-contaminated blood products still escape detection, and this still constitutes the highest post-transfusion infectious risk as exemplified by recent reports of severe and fatal reactions. Contamination cannot be avoided completely and current testing methods do not achieve 100% sensitivity.
Thus, there is a need for improved methods of preventing bacterial contamination in transfusable blood products, and especially blood products such as platelets which cannot be stored at low temperatures to curtail bacterial growth.